KR102479196B1 - Decompression and cooling systems for containment vessels in nuclear power plants - Google Patents

Abstract

With a system (90) for depressurization and cooling of vapors and/or condensable gases in containment vessel (6) - an upstream port connected to containment vessel (6) via exhaust pipe (10) and via back-feed pipe (30). The backfeed piping having a downstream port connected to the containment vessel (6) has a vapor condenser (24) with a backfeed compressor (32) - and a recooling system for recooling the vapor condenser (24). It is an object of the present invention to enable efficient recooling of the vapor condenser (24). According to the present invention this object is achieved by making the recooling system self-contained.

Description

Decompression and cooling systems for containment vessels in nuclear power plants

The present invention relates to a decompression and cooling system for a containment vessel in a nuclear power plant.

A decompression and cooling system according to the preamble of claim 1 is known from prior art WO 2014/019770 A1. The entire system connected to the containment is also known as the containment protection system. This promotes depressurization of the containment atmosphere in case of a major accident.

Accordingly, the known containment protection is

- an exhaust piping of the exhaust stream connected to the containment vessel, with a steam condenser connected to the exhaust piping;

- a backfeed line for the gaseous portion of the exhaust flow from the vapor condenser to the containment vessel, the backfeed compressor being connected to the backfeed line, and

- Re-cooling of the vapor condenser by vaporization of liquid nitrogen is provided.

Vapors and condensable gases contained in the exhaust stream are condensed in the vapor condenser. The depressurized gas portion of the exhaust stream is then fed back to the containment via a backfeed piping, to which a backfeed compressor is connected to overcome the pressure gradient. The condensate accumulated in the steam condenser is contained in a similar manner. Can be fed back to the vessel.

During operation, large amounts of heat can collect in the vapor condenser, which can adversely affect the condensation process by reducing its ability to function as a heat sink.

Known recooling of vapor condensers by vaporization of liquid nitrogen requires large amounts of stored nitrogen, which is expensive and space consuming.

It is an object of the present invention to enable effective and reliable re-cooling of the vapor condenser in the aforementioned decompression and cooling systems or containment protection systems.

According to the invention, this object is achieved by a decompression and cooling system having the features of claim 1 .

Preferred embodiments are defined in the dependent claims and the detailed description below.

A key feature of the system thus claimed is a self-sustaining cooling circuit for recooling of the steam condenser, preferably a first thermally coupled to the steam condenser. and a first heat exchanger thermally coupled to an expansion engine, a compressor pump, and a heat sink, wherein the expansion engine powers the compressor pump.

In this way, passive recooling of the steam condenser is achieved, which is based on the principle of recovery and utilization of the energy contained in the exhaust stream. The entire cooling circuit works autonomously even during startup.

A preferred embodiment of the cooling circuit includes a superheater in the cooling circuit between the first heat exchanger and the expansion engine, which is thermally coupled to the exhaust pipe to be heated by the exhaust flow. The temperature of the refrigerant is thereby increased before entering the expansion engine, so that the yield of the expansion engine is increased, with the disadvantage of introducing additional heat into the cooling circuit.

In a particularly preferred embodiment, this drawback can be compensated for by connecting a vortex cooler or vortex tube to the cooling circuit between the compressor pump and the first heat exchanger. The swirl tube is preferably a completely passive cooling device without moving parts. In this context, the vortex tube removes the excess heat introduced into the cooling circuit by the superheater. Accordingly, the temperature difference between the cold section and the hot sector of the cooling circuit increases, thereby improving overall cooling efficiency.

In a preferred embodiment, a recombiner unit is connected to the exhaust piping upstream of the vapor condenser. Recombining hydrogen with oxygen yields water vapor or steam. Alternatively or additionally, the recombiner may be configured to catalytically recombine carbon monoxide with oxygen to produce carbon dioxide.

In one useful embodiment, the cooling circuit may be configured to circulate the refrigerant in a super-critical state.

Preferably, the refrigerant circulating in the cooling circuit has a boiling temperature of less than 100 °C, preferably less than 80 °C. This supports startup and self-sustaining operation of the cooling circuit even when the driving temperature difference between the heat source and heat sink is relatively low.

A particularly suitable refrigerant is carbon dioxide.

In a preferred embodiment the expansion engine in the cooling circuit is a steam turbine.

In another preferred embodiment, the expansion engine and compressor pump are mechanically coupled to each other, preferably via a common shaft.

In another preferred embodiment, the expansion engine also operates a blower, which blower is directed at an air cooler. This improves the (cooling) capacity of the air cooler.

Preferably, the expansion engine also at least partially operates the backfeeding compressor.

The entire containment protection system is preferably designed with the goal of zero-release of radioactive material into the environment. Instead of (discharge), the gaseous portion of the exhaust vapor and preferably the condensed liquid portion are also fed back into the containment. Compared to conventional systems, there is no ventilation to the outside atmosphere by default (but you can still choose (outside ventilation)).

In general, the depressurization and cooling system/container protection system according to the present invention provides for removal of nuclear decay heat after a catastrophic accident and pressure relief of the containment without release of radioactive fission products into the environment. promote Even during a serious accident, the negative effects are confined to the plant and there is no effect on the surrounding environment (radioactive contamination). The energy content of the combustible gases (H ₂ , CO) together with the nuclear energy content (decay heat) of the containment is used in passive and self-contained processes/systems that maintain the integrity of the containment for a long period of time without an external supply of energy and refrigerant. do. Passive cooling cycles that generate surplus power can be used in many other applications where passive heat removal and cooling are required.

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.
1 shows a simplified schematic diagram of a first variant of a plant protection system according to the invention.
2 shows a second variant of the plant protection system.
3 shows a third modified example.
Figure 4 is a diagram showing the thermodynamic process employed in the plant protection system.

Looking more closely at FIG. 1, a nuclear power plant 2, shown here only in part, includes a containment wall 4 surrounding a reactor pressure vessel (not shown) and a nuclear power plant. and the relevant components of the cooling circuit. The containment wall 4 is designed to contain radioactive vapors or gases up to maximum pressure in case of emergency. The area inside the containment wall 4 is also known as containment 6.

When the pressure inside containment vessel 6 exceeds a threshold value, which typically ranges from 1 to 3 bar relative to atmospheric pressure, containment protection system 8 promotes depressurization. For this purpose, the containment protection system 8 has an exhaust line 10 for the exhaust stream. The exhaust pipe 10 has an inlet aperture inside the containment vessel 6 and penetrates the containment vessel wall 4 . During normal operation of the nuclear power plant 2 this piping is closed by means of at least one shut-off valve 12 preferably located immediately behind the containment wall 4 . To allow depressurization of the containment vessel 6, the shut-off valve 12 is opened and driven by the pressure difference between the containment vessel 6 and the low-pressure part of the exhaust pipe 12 at a pressure essentially equal to atmospheric pressure so that the exhaust flow this begins The mass flow rate of the exhaust stream is typically at a value of 2 to 10 kg/s, depending on the post-accident decay-heat in the containment (approximately 10 to 20 MW of decay heat in a 1000 to 1600 MW power plant). reach

Typically, the exhaust stream contains hydrogen (eg in >4% content), which in combination with oxygen forms an explosive gas mixture, endangering the entire plant. Therefore, the recombiner unit 14, which preferably has a plurality of passive autocatalytic recombiners, converts hydrogen and oxygen into harmless water vapor or steam. 10) is connected. Alternatively or additionally, there are also catalytic recombiners that convert carbon monoxide to carbon dioxide. The exothermic nature of the recombination process causes the exhaust steam to become hot, reaching temperatures typically in the range of 400 °C to 800 °C. The vapor portion of the exhaust flow is thus overheated in an approximately isobaric process.

The recombiner unit 14 can be located on the inside portion of the containment vessel 6 of the exhaust piping 20, but a preferred location is outside the containment vessel 6 immediately after the containment vessel 6. Excessively high temperatures in the lead-through of the containment wall 4 can then be avoided.

A flame arrestor 16 at the inlet of the recombiner unit 14 prevents accidental ignition of the gas mixture from the containment vessel 6 from propagating to the containment protection system 8 and vice versa.

Optionally, a storage container 18 of oxygen is passed through a feeding line 20 to an exhaust piping 10 or recombiner unit to increase the oxygen content in the exhaust stream when necessary/useful for a subsequent recombination process. (14) (see Fig. 3)

Downstream of the recombiner unit 14, the exhaust stream may pass through an (optional) filter unit 22, for example a particle filter or a sorbent filter.

Further downstream, the exhaust stream is led to a steam condenser 24 where the vapor portion of the exhaust flow is condensed into liquid substances. There is pressure relief associated with condensation. The vapor condenser 24 has a vessel 16 in which liquid condensate accumulates in the bottom area. The incoming exhaust stream is preferably sprayed (directly condensed) in the liquid phase (condensate) by means of a plurality of spray nozzles 28, so that the device is a washer or wet scrubber for gaseous components. ) also functions. At the start of the vent process, which is not yet condensate free, vessel 16 may be at least partially filled with an initial inventory of (auxiliary) cooling liquid.

The non-condensable gaseous portion of the exhaust stream accumulates in the gas space in the upper region of vessel 26 above the liquid phase (condensate). From there it is fed back to the containment vessel 26 through a backfeed line 30 to which a backfeed compressor 32 is connected to overcome the pressure difference.

Another backfeed pipe 34 attached to the bottom of the vessel 26 allows the liquid condensate to be fed back to the containment vessel 6 by the backfeed pump 36.

A first heat exchanger 40, an expansion engine 42, a second heat exchanger 44, and a compressor pump 46 for the purpose of re-cooling the steam condenser 24 There is a self-sustaining cooling circuit 38 comprising:

The first heat exchanger 40 is thermally coupled to the vapor condenser 240 and functions as a heater for the refrigerant/heat transfer medium circulating in the cooling circuit 38. Preferably, the first heat exchanger 4 It is located inside the area normally filled with liquid during the evacuation/ventilation operation of the containment protection system 8 in the vessel 26. In other words, the first heat exchanger 40 preferably accumulates in the vapor condenser 24. immersed in a liquid that serves as a heat source.

The expansion engine 42 located downstream of the first heat exchanger 40 in the cooling circuit 38 is preferably a steam turbine. The heated refrigerant is expanded in the expansion organ 42 and energy is converted into mechanical work.

Further downstream, there is a second heat exchanger 44 that is connected to the surrounding environment and functions as a cooler for the expanded refrigerant. This is preferably implemented as an air cooler. That is, the excess heat contained in the refrigerant is transferred to the surrounding atmosphere/environment, which acts as a heat sink.

Further downstream, the expanded and recooled refrigerant is passed through a compressor pump 46 which drives a cooling circuit 38 on the principle of forced circulation, preferably in a turbo-compressor manner.

Then, the refrigerant is led back to the first heat exchanger 40 so that the cooling circuit 38 is closed.

Accordingly, the cooling circuit 38 has a first heat exchanger 40 thermally coupled to the vapor condenser 24 (typical temperature: 90 °C) and a second heat exchanger thermally coupled to the surrounding environment (typical temperature: 20 to 40 °C). It forms a closed thermodynamic cycle efficiently driven by the heat difference between the groups 44.

In a possible implementation, the cooling circuit 38 is a two-phase (heater) functioning as an evaporator for the refrigerant and the second heat exchanger 44 (cooler) functioning as a condenser. It is a two-phase circuit. In this case, the refrigerant preferably has a boiling temperature of less than 100 °C, more preferably less than 80 °C to match the typical temperature range of the heat source in the vapor condenser 24.

However, in a preferred embodiment, the cooling circuit 38 is designed to circulate the refrigerant/liquid in a super-critical state. A suitable refrigerant for this purpose is, for example, carbon dioxide (CO ₂ ) with a critical temperature of 31.0° C. and a critical pressure of 73.8 bar. That is, the cooling circuit 38 must be designed to withstand these high pressures above the critical pressure. The supercritical mode of operation is advantageous because of the high density of the refrigerant with a correspondingly high heat transfer capability and still high fluidity in the piping system of the cooling circuit 38.

The underlying Joule process for a supercritical fluid, here a carbon dioxide-based refrigerant, is visualized in the diagram of FIG. 4, where pressure p is plotted against enthalpy (h) (p-h diagram). The expansion of the liquid in the expansion engine 42 and the compression by the compressor pump 46 are approximately isentropic processes, whereas the heating and cooling in the corresponding heat exchangers 40 and 440 are approximately isobaric processes. , this kind of process control is particularly suitable for high yields of excess energy available.

Referring again to Figure 1, for self-contained operation of the cooling circuit 38, the expansion engine 42 operates the compressor pump 46. This is preferably achieved by mechanically coupling the expansion engine 42 and the compressor pump 46 to each other, preferably via a common shaft, and if necessary to include transmission gearing therebetween. can However, other variants are also possible, for example through the generation of electrical energy with the aid of a generator 48 . The generated electricity can then drive the motor of the compressor pump 46 . If necessary, temporary storage of electrical energy in suitable storage units, such as accumulators, may also take place.

For efficient operation, an additional heat exchanger 50 can be connected downstream of the first heat exchanger 40 and upstream of the expansion engine 42 of the cooling circuit. The secondary side of the heat exchanger 50 is the portion of the exhaust piping 10 between the recombiner unit 14 and the vapor condenser 24 so that a branch stream of the hot exhaust stream serves as a heating medium. connected to the hot part. Dedicated throttle valve 52 (see FIG. 2 ) and/or filter unit 22 (see FIG. 1 ) and/or steam turbine 66 (see FIG. 3 ) of exhaust piping 10 , etc. Another device in the throttle acts as a throttle allowing the branch stream to be fed back into the main exhaust stream before the steam condenser 80 without active means of drive. This means that the supply pipe 80 of the heat exchanger 50 is a branch pipe from the exhaust pipe 10 before the throttle section (viewed in the direction of the exhaust flow), and the return pipe 82 is the exhaust pipe after the throttle section ( 10) to be integrated.

As such, the additional heat exchanger 50 functions as a recuperative superheater before the refrigerant circulating in the cooling circuit 38 enters the expansion engine 42 . This improves the yield of the expansion engine 42 at the potential disadvantage of introducing additional heat into the cooling circuit 38 .

In one preferred embodiment shown in FIG. 2, a vortex cooler 54 is downstream of the compressor pump 46 to further cool the cooling medium before re-entering the first heat exchanger 40 in the main heat source. installed The vortex cooler 54 or vortex tube is a mechanical device that separates a fluid stream into hot and cold branched streams by vortex flow without moving parts. The cold flow then enters the first heat exchanger (40) through the cold fluid pipe (56) and the hot branch flow through the hot fluid pipe (58) just before the superheater (50) or back to the main cooling loop of the superheater. is sprayed It has been demonstrated that in this way the aforementioned disadvantages are compensated for or eliminated and the overall cooling efficiency of the system is improved.

Inside the swirl tube, a pressurized fluid is injected tangentially into a swirl chamber 60 and accelerated to a high rotational speed. Because of the conical nozzle 62 at the end of the tube, only the outer shell of the pressurized fluid is allowed to escape at that end. The remainder of the fluid is forced back into an inner vortex of reduced diameter inside the outer vortex. Although the cooling efficiency of this device is relatively low, the device is completely passive with no moving parts.

In the preferred embodiment shown in both Figures 1 and 2, the expansion engine 42 also operates a blower 64 directed at the second heat exchanger 44 (aka air cooler) to improve its cooling efficiency. let it This may be done through a mechanical coupling or indirectly by electrical energy generated in generator 48 as shown.

In a similar manner, expansion engine 420 may at least partially actuate backfeeding compressor 32 and/or backfeeding pump 36 .

The variant of the containment protection system shown in FIG. 3 differs from the variant of FIG. 1 in that a steam turbine 66 is connected to the exhaust piping 10 between the recombiner unit 914 and the steam condenser 24 . The steam turbine 66 converts a portion of the thermal energy contained in the exhaust stream into mechanical work for at least partially driving the backfeeding compressor 32 and/or the backfeeding pump 36 (roughly an isentropic process). . This may be achieved directly, for example, through mechanical coupling of the steam turbine 66 with the backfeeding compressor 32 and/or the backfeeding pump 36, and/or indirectly through the generation of electrical energy by the generator 68. there is. This is also possible with a turbine-compressor-generator unit on a single shaft. If necessary, temporary storage of electrical energy may also be effected in a suitable storage unit, such as an accumulator.

In addition, mechanical and/or electrical power generated by steam turbine 66 may be used to at least partially drive compressor pump 46 and/or blower 64 of refrigeration circuit 38 .

In general, the recoverable excess energy depends on the hydrogen content contained in the exhaust stream and on the power required for the backfeed pump 32, which in turn depends on the pressure difference between the containment vessel 6 and the steam condenser 24 during ventilation operation. do.

In the embodiment according to FIG. 3 , the supply pipe 80 for the superheater 50 is attached to the exhaust pipe 10 upstream of the steam turbine 66 , while the return pipe 82 is attached downstream.

The vortex cooler 54 described in FIG. 2 can also be used in the same way in the embodiment according to FIG. 3 .

The entire containment protection system 8 or parts thereof may be installed inside the containment vessel 6 if the available space inside the containment vessel 6 is sufficiently large.

Parts of the containment protection system 8 that target depressurization and cooling are also known as decompression and cooling systems 90.

As is clear from the above description. Various features of each figure may be combined with various features of other figures.

The nuclear power plant can be of any known type, such as BWR, PWR, WWER, HWR, HTR.

2: power plant
4: containment wall
6: containment
8: containment protection system
10: exhaust line
12: shut-off valve
14: recombiner unit
16: flame arrestor
18: storage container
20: feeding line
22: filter unit
24: steam condenser
26: container
28: nozzle
30: backfeed line
32: backfeed compressor
34: backfeed line
36: backfeed pump
38: cooling circuit
40: first heat exchanger
42: expansion engine
44: second heat exchanger
46: compressor pump
48: generator
50: heat exchanger (superheater)
52: throttle valve
54: vortex cooler
56: cold fluid line
58: hot fluid line
60: swirl chamber
62: conical nozzle
64: blower
66: steam turbine
68: generator
80: feeding line
82: return line
90: depressurization and cooling system

Claims (23)

With a depressurization and cooling system (90) of vapors and/or condensable gases in the atmosphere in the containment vessel (6),
- as a vapor condenser (24),
- an upstream port connected to the containment vessel (6) through the exhaust pipe (10);
- a downstream port connected to the containment vessel (6) through a backflow pipe (30);
- a vapor condenser (24) comprising said backfeed piping with a backfeed compressor (32);
- with a recooling system for recooling the vapor condenser (24);
wherein the recooling system comprises a closed loop working fluid thermodynamic cycle, wherein the vapor condenser (24) is a heat source;
The recooling system is in a closed loop in which the working fluid circulates:
- a first heat exchanger (40) thermally coupled to the vapor condenser (24);
- an expansion engine (42) fluidly connected to the first heat exchanger (40);
- a second heat exchanger (44) fluidly connected to the expansion engine (42);
- a compressor pump (46) fluidly connected downstream of the second heat exchanger (44) and upstream of the first heat exchanger (40);
- a superheater (50) connected downstream of the first heat exchanger (40) and upstream of the expansion engine (42);
Decompression and cooling system (90), characterized in that the expansion engine (42) operates the compressor pump (46) and the superheater (50) is thermally coupled to the exhaust pipe (10) such that it is heated by the exhaust stream. . In claim 1,
A decompression and cooling system (90) wherein the recooling system includes a vortex cooler (54) fluidly connected downstream of the compressor pump (46) and upstream of the first heat exchanger (40). In claim 2,
A decompression and cooling system (90) in which the vortex cooler (54) has a hot fluid outlet connected to the region of the recooling system downstream of the first heat exchanger (40) and upstream of the expansion tube (42). In claim 1,
A decompression and cooling system (90) in which the exhaust piping (10) has a recombiner unit (14) upstream of the vapor condenser (24). In a containment protection system (8) for a power plant (2) having a containment vessel (6),
- an exhaust piping (10) connected to the containment vessel (6), to which the vapor condenser (24) is switched, and for a containment atmosphere exhaust stream;
- a backfeed piping (30) for the gas portion of the containment atmospheric exhaust flow from the vapor condenser (24) to the containment vessel (6), to which the backfeed compressor (32) is switched;
- a cooling circuit (38) for recooling the vapor condenser (24),
The cooling circuit (38) has a first heat exchanger (40) thermally coupled to the vapor condenser (24) and a second heat exchanger (40) thermally coupled to the expansion engine (42), the compressor pump (46) and a heat sink. a superheater (50) in the cooling circuit (38) between the first heat exchanger (40) and the expansion engine (42); and characterized in that the superheater (50) is thermally coupled to the exhaust piping (10) such that it is heated by the containment atmosphere exhaust flow. In claim 5,
A containment protection system (8) with a vortex cooler (54) in the cooling circuit (38) between the compressor pump (46) and the first heat exchanger (40). In claim 6,
A containment protection system (8) wherein the vortex cooler (54) has a hot fluid outlet fluidly connected to a cooling circuit (38) in the region between the first heat exchanger (40) and the expansion engine (42). In claim 5,
A containment protection system (8) in which the recombiner unit (14) is connected to the exhaust piping (10) upstream of the vapor condenser (24). In claim 5,
A containment protection system (8) in which the second heat exchanger (44) is implemented as an air cooler. In claim 5,
A containment protection system (8) wherein the cooling circuit (38) is configured to circulate the refrigerant in a supercritical state. In claim 5,
A containment protection system (8) in which the refrigerant has a boiling temperature of less than 100 °C. In claim 5,
A containment protection system where the refrigerant is carbon dioxide (8). In claim 5,
A containment protection system (8) in which the expansion engine (42) is a steam turbine. In claim 5,
A containment protection system (8) in which the expansion engine (42) and the compressor pump (46) are mechanically coupled to each other via a common shaft. In claim 5,
The containment protection system (8), in which the expansion engine (42) also operates the blower (64), which blower (64) is directed towards the second heat exchanger (44). In claim 5,
The containment protection system (8) in which the expansion engine (42) further operates the back-feeding compressor (32). In claim 5,
A containment protection system (8) designed for zero release of radioactive material into the surrounding environment. A nuclear power plant (2) having a containment vessel (6) and a decompression and cooling system (90) according to any one of claims 1 to 4 or a containment protection system (8) according to any one of claims 5 to 17. delete delete delete delete delete

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